The most common time I’m asked the question of how to identify moisture issues is when someone buys an existing straw bale house. Moisture is not often a problem in straw bale homes as long as the house was built well. That said, there may be issues that show up over time. Here are some basic things to assessing moisture in a straw bale wall.
Take a look around the lower corners of the windows for signs of moisture damage. This is the most common area that moisture damage occurs. Check inside and out in this area. You’ll see staining on the plaster, or worse, buckling and peeling plaster.
Anywhere there is a penetration (electrical plugs are the most obvious), take a strong smell and see if you get a hint of damp. In most cases you won’t.
If you believe there is moisture damage, the best thing to do is drill some small holes in the plaster in the suspect areas and insert the probe of a moisture meter. Any readings over 20% are bad and can sustain mold growth. I would want to see readings around 12%. If you do have moisture problems, you’ll need to push some dry heat through the wall while it’s hot and dry outside as well, if possible. The key will be finding the source for the moisture and that will dictate how hard of a fix it will be.